Issue 40, 2023

Solvatochromic and aggregation-induced emission active nitrophenyl-substituted pyrrolidinone-fused-1,2-azaborine with a pre-twisted molecular geometry

Abstract

Boron–nitrogen-containing heterocycles with extended conjugated π-systems such as polycyclic aromatic 1,2-azaborines, hold the fascination of organic chemists due to their unique optoelectronic properties. However, the majority of polycyclic aromatic 1,2-azaborines aggregate at high concentrations or in the solid-state, resulting in aggregation-caused quenching (ACQ) of emission. This practical limitation poses significant challenges for polycyclic aromatic 1,2-azaborines’ use in many applications. Additionally, only a few solvatochromic polycyclic aromatic 1,2-azaborines have been reported and they all display minimal solvatochromism. Therefore, the scope of available polycyclic 1,2-azaborines needs to be expanded to include those displaying fluorescence at high concentration and in the solid-state as well as those that exhibit significant changes in emission intensity in various solvents due to different polarities. To address the ACQ issue, we evaluate the effect of a pre-twisted molecular geometry on the optoelectronic properties of polycyclic aromatic 1,2-azaborines. Specifically, three phenyl-substituted pyrrolidinone-fused 1,2-azaborines (PFAs) with similar structures and functionalized with diverse electronic moieties (–H, –NO2, –CN, referred to as PFA 1, 2, and 3, respectively) were experimentally and computationally studied. Interestingly, PFA 2 displays two distinct emission properties: (1) solvatochromism, in which its emission and quantum yields are tunable with respect to solvent polarity, and (2) fluorescence that can be completely “turned off” and “turned on” via aggregation-induced emission (AIE). This report provides the first example of a polycyclic aromatic 1,2-azaborine that displays both AIE and solvatochromism properties in a single BN-substituted backbone. According to time-dependent density functional theory (TD-DFT) calculations, the fluorescence properties of PFA 2 can be explained by the presence of a low-lying n–π* charge transfer state inaccessible to PFA 1 or PFA 3. These findings will help in the design of future polycyclic aromatic 1,2-azaborines that are solvatochromic and AIE-active as well as in understanding how molecular geometry affects these compounds’ optoelectronic properties.

Graphical abstract: Solvatochromic and aggregation-induced emission active nitrophenyl-substituted pyrrolidinone-fused-1,2-azaborine with a pre-twisted molecular geometry

  • This article is part of the themed collection: #MyFirstJMCC

Supplementary files

Article information

Article type
Paper
Submitted
10 Ira. 2023
Accepted
12 Ira. 2023
First published
13 Ira. 2023

J. Mater. Chem. C, 2023,11, 13740-13751

Author version available

Solvatochromic and aggregation-induced emission active nitrophenyl-substituted pyrrolidinone-fused-1,2-azaborine with a pre-twisted molecular geometry

A. D. Campbell, K. Ellis, L. K. Gordon, J. E. Riley, V. Le, K. K. Hollister, S. O. Ajagbe, S. Gozem, R. B. Hughley, A. M. Boswell, O. Adjei-sah, P. D. Baruah, R. Malone, L. M. Whitt, R. J. Gilliard and C. J. Saint-Louis, J. Mater. Chem. C, 2023, 11, 13740 DOI: 10.1039/D3TC03278G

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